1. Field of the Invention
The present invention relates to a lens body tube of a zooming optical system applicable to apparatuses and devices in various kinds of fields requiring the zooming optical system such as a normal camera using a silver salt film, a video camera, a projector, etc. More particularly, the present invention relates to a lens body tube having a zooming optical system in which a specified focal length unable to be obtained by only the zooming optical system can be realized by detachably attaching and inserting a converter lens into the zooming optical system to change its focal length while a plurality of lens groups are relatively moved on an optical axis of the zooming optical system.
2. Description of the Related Art
For example, each of Japanese Patent Application Laying Open (KOKAI) Nos. 2-302711, 2-308113, 2-308210, 2-308211, 2-308212, 3-6971 and 3-11312 shows a technique of a lens body tube with a built-in zooming optical system in which a specified focal length unable to be obtained by only the zooming optical system can be realized by detachably attaching and inserting a converter lens into the zooming optical system. This specified focal length is provided at a super wide angle or a super telescopic end.
However, in the technique of the lens body tube shown by each of these publications, it is often necessary to arrange a dedicated operating member used to take a super wide angle photograph or a super telescopic photograph in addition to an operating member such as a seesaw knob used to take a photograph in a zooming region. An electric driving means such as an electric motor and a solenoid for attaching and detaching the converter lens is separately required in addition to a driving means for zooming even when no dedicated operating member is required. Further, a special electric control means for attaching and detaching the converter lens is required when no dedicated operating member is required. Operability of the lens body tube is reduced by these problems. Otherwise, a structure of the lens body tube becomes complicated mainly by these problems.
In the technique shown in each of the above publications, the structure of a mechanical moving means for attaching and detaching the converter lens becomes complicated so that the structure of the lens body tube is further complicated.
Each of the above publications does not show any problems and techniques for reducing a length of the lens body tube when no lens body tube is used. Therefore, each of these publications cannot be used as a reference technique for obtaining a lens body tube reduced in length.